Hi Megatron
First off I'm not a financial adviser, so this isn't gospel!
I'd say make sure you don't have expensive debts (credit cards in particular; mortgages tend not to be so bad) and that you have enough in cash (and readily accessible, so not in some 2-year fixed rate bond at the building society) to meet say 3 months' outgoings in case of financial disaster.
What you do with the rest will depend on your attitude to risk. Shares have historically had the best long-term growth potential, and you can buy funds (either closed-end/investment trusts or open-end/unit trusts) where a manager chooses lots of shares for you so you don't have to do it yourself. There are also multi-manager funds which are basically funds that invest in other funds. Just as holding a fund is less risky than just holding one share (if it goes bust you lose all your money but the chances of all the companies in a fund going bust are - hopefully - slim), a fund of funds should be less risky than a single fund.
For a long-term 'buy and forget' sort of a fund, you might consider a big, globally diversified investment trust like Foreign & Colonial or Witan. They have been around for donkey's years and charges on investment trusts tend to be lower than on open-ended funds.
Managed funds (which include funds of funds mentioned earlier) might work for you too. Miton (I think they are called MAM Funds these days) and Ruffer are good at this. I think you can buy their funds through a big broker like Hargreaves Lansdown.
If you go to see a financial adviser, try to find one who works on a fee not on commission. That way they won't be biased in their choices and your money will be working for you, not them. www.unbiased.co.uk is a good place to find an IFA.
You can put just over £10k a year in an Individual Savings Account (ISA) which means you don't pay any tax on the income from or growth in the investments. All the funds I have mentioned can be held in an ISA.
Finally, I suppose £40k might be enough for a deposit on a buy-to-let property if you're into that kind of thing, though then you'll have ongoing responsibilities in terms of tenants and so on.
Best of luck!